Leakage recovering mechanism for hydraulic brake booster mechanisms



June 8, 1954 E. G. HM ETAL 2,680,349

LEAKAGE RECOVERING MECHANISM FOR HYDRAULIC BRAKE BOOSTER MECHANISMS June 8, 1954 E. G. HILL ErAL 2,680,349

LEAKAGE RECOVERING MECHANISM FOR HYDRAULIC BRAKE BOOSTER MECHANISMS Filed Feb. 26, 1948 2 Sheets-Sheet 2 Ell- T..E

Patented June 8, 1954 UNITED STATES PATENT OFFICE LEAKAG RECOVERING MECHNISM FOR HYDRAULIC BRAKE BOOSTERl MECH- ANISMS poration of Delaware Application February 26, 1948, Serial No. 11,056

(Cl. (iO-54.5)

12 Claims. 1 'I'his invention relates to a mechanism for collecting hydraulic leakage uid from a hydraulic mechanism and returning it to thesource of such iiuid, and has particular reference to the collection of leakage fluid from a booster brake mechanism for motor vehicles and the returning of such fluid to the reservoir of the master cylinder.

A number of commercially practicable booster brake mechanisms for motor vehicles have been developed wherein a booster motor, usually vacuum operated, is energized by the displacement of hydraulic fluid from the master cylinder and creates, or assists the pedal effort in creating, a relatively high hydraulic pressure for applying the vehicle brakes. Such brake applying pressure is usually directly generated by a piston movable in a high pressure cylinder. This piston is provided with a sealing cup engageable with the walls of the cylinder to coni-lne the hydraulic uid in the high pressure chamber during the generation of pressure therein.

The sealing means employed are adequate to the extent that booster brake mechanisms are fully operative and highly practicable, but so far as we are aware, no perfect sealing cup has been developed. There is always some leakage past the sealing cup and this leakage fluid is lost from the system with resulting serious trouble which has caused serious accidents to occur. Most booster brake mechanisms are so constructed that upon each releasing of the brakes, the leakage fluid has been compensated for by returning to the high pressure end of the system an amount of fluid equal to that which has leaked from the high pressure end of the system. This replacement fluid is derived from the reservoir of the master cylinder and a number of instances have occurred in practice in which the reservoirs have been emptied in a comparatively short time, and in fact, in a much shorter time than ordinarily would occur. The driver receives no warning of such loss of fluid by leakage, the uid in commercial booster brake installations finding its way into a vacuum chamber of the booster motor from which it is drawn into the intake manifold of the engine to be burned and exhausted. It has occurred, therefore, that, without his being aware that the reservoir has been drained of fluid, the operator has depressed the brake pedal with a resultant lack of brake application due to insufficient fluid in the system. Serious accidents have occurred from this cause.

Motor vehicles and booster' brake manufacturershave been aware of the difficulties referred to and strenuous eiorts have been made to overcome the defect. Most of these efforts have been quite naturally directed toward improvement in the sealing cups, but no perfect seal has been found, so far as we are aware. It has been proposed to drill a drain opening'in the space behind the high pressure piston to drain out leakage fluid, but this is of little assistance since the hydraulic fluid is merely lost without warning to the operator. This expedient is slightly helpful in commercial booster brake .f mechanisms for the reason that it vents the space behind the high pressure piston to the atmosphere. This reduces differential pressures on opposite sides of the high pressure piston, the back of which is usually subjected to vacuum in the booster motor. However, the eX- pedient referred to merely reduces leakage but does not eliminate it and does not salvage the leakage fluid.

An important object of the present invention is to provide a novel and wholly automatic mechanism which collects fluid leaking from a hydraulic system and returns it to the source of such fluid, thus preventing losses of fluid from the system regardless of the extent of the leakage past hydraulic pressure pistons.

A further object is to provide a mechanism of the character referred to which is particularly adapted for use with hydraulic booster ,mechanisms for motor vehicles for collecting fluid which leaks past the high pressure hydraulic piston and returns the uid to the reservoir of the master cylinder, thus preventing loss of hydraulic fluid from the system.

A further object is to provide in combination with a hydraulic booster brake mechanism, a device for utilizing varying pressures occurring at one side of the piston which is actuated by fluid displaced from the master cylinder for 'withdrawing from the high pressure cylinder fluid which has leaked past the high pressure piston and for returning such fluid to the reservoir of the master cylinder.

Other objects and advantages of the invention will become apparent during the course of the following description.

In the drawings I have shown one embodiment of the invention. In this showing:

Figure 1 is an axial sectional View through a hydraulic booster mechanism showing the invention applied, the master cylinder and the Wheel brake cylinder being represented,

diagrammaticallyv Figure 2 is an enlarged fragmentary sectional view of the high pressure end of the booster mechanism and associated elements,

Figure 3 is a face view of a portion of the pressure-responsive member of the booster motor showing the valve operating elements associated therewith, and,

Figure 4 is a detail sectional View on line d--ll of Figure 3.

Referring to Figure 1, the numeral I designates the vehicle master cylinder as a whole having the usual reservoir II and piston (not shown) operable by a conventional brake pedal I2 to displace hydraulic fluid through a line I3 to operate the motor vehicle brakes'. These elements, of course, are conventional and need not be shown in detail.

The line I3 leads through a suitable connection I5 to supply hydraulic brake fluid to a booster mechanism indicated as a whole by the numeral I6, the brake fluid being delivered into one end of a low pressure cylinder I1 forming a part of the booster mechanism. The lov.1 pressure cylinder and the elements associated therewith will be referred to later.

Through means to be described, relatively high pressure is developed in a high pressure hydraulic cylinder 241 having a suitable connection 2i leading to a pipe line 22 for delivering hydraulic iluid to the usual brake cylinders 23 to apply the brakes. The high pressure cylinder 2B and associated elements also will be referred to in detail later.

A booster motor indicated as a whole by the numeral 25 assists the operator in generating pressure in the cylinder 20. This motor comprises casing sections 26 and 21 in which is arranged a pressure-responsive member 2S comprising a rigid plate portion 29 and a flexible radially outer diaphragm portion 30 having a peripheral bead 3l arranged between flanges 32 formed on the casing sections 25 and 21. These anges and the bead BI are maintained in clamped relation by a split clamping band 33. The remote ends of the casing sections 26 and 21 are secured respectively to the cylinders I1 and 2i! and these cylinders, in the present embodiment of the invention, are arranged in axial alinement. The booster motor25 in the present instance, is vacuum suspended. The casing sections 23 and 21 are divided by the pressure-responsive member 28 to form a variable pressure chamber 35 and a constant pressure vacuum chamber 33 in constant communication with a source of partial vacuum. For this purpose, the casing section 21 is provided with a nipple 38 connected by a suitable line Se to the intake manifold 40 of the vehicle engine. The chambers 35 and 35 normally communicate with each other to vacuum suspend the pressure-responsive unit 28, and this communication is cut olf and air admitted into the chamber 35 to actuate the pressure-responsive unit 28 in a manner to be described.

Referring to Figure 4, it will be noted that a suitable valve mechanism for the motor 25 is illustrated. The plate 29 is provided with a valve insert 45 having a seat 46 normally closed by a ball valve 41, thus closing communication between the chamber 35 and a recess 4B formed in a boss 49 cast integral with the plate 29. A nipple 50 is threaded into the boss 43 to connect the recess 48 to one end of a flexible hose 5I, the Y opposite end of which is connected by an elbow 52 to a nipple 53 communicating with the atmosphere, preferably by a small air cleaner (not shown) adapted to be threaded on the nipple 53.

The plate 29 is provided with a second valve insert 56 having an axial passage 51 therethrough, one end of which forms a seat 58 engageable by a valve 53. The stem 60 of this valve extends through and beyond the opening 51 as shown in Figure 4 and projects loosely through a valve operating plate 62. A suitable nut 63 is threaded on the stern 60 and limits movement of the valve 59 from the plate 62, and a small spring @il is arranged between the plate 62 and valve Se to urge the latter away from the plate 62 to the extent limited by the nut 63.

The plate 62 is substantially triangular as shown in Figure 3 and the stem 6G projects through one of the upper corners of such plate. The other upper corner of the plate engages the ball 1, as shown in Figures 3 and 4.

The plate 62 is provided with a stamped recess 68 receiving a hemispherical boss 69 carried by the plate 29. This boss 69 serves as a rocking pivot for the plate 62 and permits the plate to rock on a line between the point of contact of the plate B2 with the ball 41 and boss B9 to close the valve 59. This disconnects the chambers .'55 and 36, as will be apparent. Further operation of the plate 62 in a manner to be described causes it to pivot on a line between the boss 59 and the point of contact of the plate 62 with the nut 53 to relieve pressure between the plate 62 and ball l1 whereby the latter will be pushed from its seat by air pressure behind the ball 41, thus admitting air from the hose 5I and recess d3 into the chamber 35. Thus the pressure-responsive unit 29 will be subjected to differential pressures to move it to the right, as viewed in Figure l.

The pressure-responsive unit 2@ further comprises a preferably integral piston sleeve 12 which projects into the high pressure cylinder 2li, as shown in Figure 1, the parts in such cylinder being shown in a partially brake-applying position, for a purpose to be described.

Referring to Figure 2, it will be noted that the sleeve 12 has its inner end abutting a ring 13 and an annular recess 14 in the end of the sleeve 12 surrounds a snap ring 15 carried by an inner coaxial tubular piston 16. A sealing cup 11 is engaged by the ring 13 and has flanges 13 and 19 respectively engaging the interior wall of the high pressure cylinder 28 and the outer surface of the tubular piston 16. A snap ring Si? prevents substantial axial displacement of the sealing cup 11.

At its inner end, the high pressure cylinder 2i) is provided with an internally threaded cap 35 for clamping a sealing cup in position. rhis cup engages the outer surface of the piston sleeve 12 to prevent leakage into the chamber 35 of any brake fluid in the space 31 behind the piston formed by the sealing cup 'I1 and associated elements.

In this connection, it is pointed out that most of the trouble which has been encountered with booster brake mechanisms vof the present type has been due to leakage of brake fluid past sealing cups corresponding to the cup 11. Such fluid finds its way into the vacuum chamber of the booster motor, and thence into the brake manifold to be burned in the vehicle engine and discharged. The present invention is particularly directed to the overcoming of such difculty and its attendant disadvantages, as further discussed below.

The tubular piston 15 has its left hand end as viewed in Figure 1 projecting into the low pressure cylinder l1 and terminates in a piston formed by an annular ring 9U backed up by a snap ring 9| and engaging a sealing cup 92. Leakage past the cup 92 usually is not serious since pressures developed in the low pressure cylinder I1 are much lower than pressures developed in the high pressure cylinder 20. For the purpose of the present invention, however, a cap 93 is threaded on the end of the cylinder I 1 within the chamber 35 and clamps in position a sealing cup 9d engaging the tubular piston 15. Between this cup and the ring 9|) is a space 95 forming a part of the interior of the low pressure cylinder, and this space is utilized in the operation of the present invention in a manner to be described.

The tubular piston 16 has an axial passage I extending therethroughv from end to end and a rod IUI extends through this passage and is adapted to engage a portion of the fitting I5 to limit movement of the rod to the left as viewed in Figure 1. The right end of the passa-ge IGS (Figure 2) is enlarged as at |02 to form a valve seat |63 normally engaged by a ball |114 urged to closed position by a spring |55. The outer end of this spring engages a cross pin |53. During energization of the booster, the valve ii is closed, and when the oif position is reached, the rod IGI unseats the ball |54 to open communication between the high and low pressure cylinders I 'I and 25 to replace leakage fluid, as will be understood. In the application of the brakes, fluid displaced from the master cylinder moves the piston sleeve 16 toward the right, as viewed in Figure l, and an annular flange |06 (Figure 1) engages the lower end of the valve operating plate S2 to rock this plate on the first and second axes referred to above to close the valve 53 and then release the valve i1 to be opened. This valve pivoting movement is opposed by a spring |99 (Figure 3) carried by the plate 29 and having its tension adjustable by a screw IIS. This particular feature forms no part per se of the present invention, but corresponds generally to the valve mechanism disclosed in the copending application of O. M. Whitten Serial No. 605,119, led July 14, 1945, now Patent No. 2,462,015.

The operation referred to energizes the motor 25 to move the piston sleeve 12 toward the right, this piston moving in a follow-up action relative to 'the tubular piston 16 whereby the booster motor cooperates with the manually operated piston sleeve to generate relatively high pressures in the high pressure cylinder 2|). This operation is fully disclosed in the prior patent to Rudolph J. Klimkiewicz No. 2,377,699, granted June 5, 1945, and need not be specifically referred to in connection with the operation of the present invention. When the brakes are released, the parts are returned to position by the pressure of the displaced fluid in the brake cylinders and brake lines 22, assisted by the usual return spring |59 (Figure 1) The mechanism forming the primary subject matter of the present invention has to do with the recovery of hydraulic fluid leakage from the space 81 (Figure 2) and the returning of such fluid to the reservoir to prevent the loss of such flm'd. Referring to Figure 2, the wall of the cylinder 2d is provided, preferably in the top thereof when the device is in the preferred position shown, with a longitudinal air passage H5 which communicates with the space 81 adjacent the sealing cap 86 through an annular groove ||6. A nipple ||8 is threaded into the body of the cylinder 20 to communicate with the passage I|5 and has an apertured plug ||9 engaged by a ball check valve |25 urged to closed position by a very light spring |2I. It will be obvious that when the pistons move to the right upon energization of the booster, substantially atmospheric pressure will be maintained in the space 81. 'I'he advantage of this will be further referred to later.

Preferably along the bottom of the cylinder 20 when the device is in the preferred position, is formed a longitudinal passage |25 communicating with the space 81 adjacent the sealing cup 86 through groove H6. The passage |25 provides for the egress of hydraulic brake fluid from the space 81 as the parts return to normal position after a brake application.

In addition to the groove H6, the space 81 preferably communicates with the passage ||5 through an opening |25 (Figure 2). This opening is unnecessary when the apparatus is used in the horizontal position in Figure 1. In some installations, however, the apparatus is arranged vertically with the right hand end as viewed in Figure 2 arranged at the top. Under such conditions, hydraulic brake fluid would accumulate along the bottom of the space 81, that is, on the seal 83. In order to prevent agitation and foaming of the hydraulic fluid under such conditions, the opening |26 is provided to vent the space 31 to the passage I I5 above the level of accumulated hydraulic fluid in the space 81.

The passage |25 externally of the casing section 21 communicates with the interior of a nipple |21 having an outwardly opening ball check Valve |23 normally held closed by a very light spring |29. The nipple |21 is in the form of a T, one run of which communicates with the passage |25 and the other run of which is connected to one end of a pipe |30 for a purpose to be described. The branch of the T is provided with a port |3| normally closed by a ball check valve |32 normally lightly maintained on its seat by a spring |33. The branch of the T is connected to one end of a pipe line |34 leading back to the reservoir I to return leakage fluid thereto.

The body of the cylinder I1 is provided with a longitudinal passage |38 communicating as at |39 with the space 95 adjacent the sealing cup 94. Externally of the casing section 25, the p-assage |33 has its left hand end, as viewed in Figure 1, communicating with the pipe |30.

Operation The booster mechanism as a whole is conventional and is constructed and operated substantially in accordance with the disclosure of the Klimkiewicz patent referred to above. The booster operation accordingly need be only briefly described. The two pistons normally occupy positions at the left hand end 0f their strokes with the rod itil engaging the fitting I5 to unseat the ball IM. Upon operation of the brake pedal, iiuid is displaced from the master cylinder into the low pressure cylinder I1 to move the tubular piston 16. The right hand end of this piston starts to move in the high pressure cylinder 2|), and the movement of the tubular piston rocks the valve plate 62 in the manner described to energize the motor 25. The pressure responsive unit 23 then moves toward the right in a follow-up action relative to the tubular piston 13, and accordingly this piston and the piston sleeve 12 move substantially in unison to build up the desired braking pressure in the high pressure cylinder 28. Hydraulic fluid from this cylinder will be displaced under pressure to the brake cylinders to apply the brakes in the usual manner.

Much experimental work has been carried on in an effort to improve the sealing characteristics of the piston cups such as the cup il to seal the high pressure cylinders of booster mechanisms against leakage. 'I'hese efforts have been attended with only limited success, and this leakage has been a source of difiiculty with booster mechanisms of this type which are now in extensive use.

Fluid leaking past the packing cup Ti finds its way into the constant vacuum chamber 3E of the booster motor, and ultimately into the intake manifold through the line 39. This leakage fluid is burned in the motor and thus lost, and in practice it has been found that the supply of hydraulic brake fluid is depleted more rapidly than is normal for braking systems Which do not include boosters. This depletion of the supply of hydraulic brake fluid in the master cylinder reservoirs has resulted in a number of serious accidents through application of the brakes With insuicient hydraulic uid available for braking use. This situation is aggravated in conventional boosters because of the fact that relatively high pressure exists in the pressure end of the cylinder 2Q while vacuum exists adjacent the opposite side of the packing cups, this vacuum being present in the motor chamber 36. The high dilerential pressures to which the sealing cups are subjected obviously aggravates the leakage cccurring with each substantial brake application. This situation has not been cured or even remedied to any substantial extent through efforts to improve the sealing cups themselves.

The present construction completely eliminates the difficulty referred to. By providing the sealcup S6 (Figure 2) and permitting the flow of air into the space S1 around check valve |29, it is impossible to subject the sealing cup 'il' to the high differential pressures normally present in an apparatus of this character. Thus leakage is minimized by the admission of air into the space 8l.

However, it is highly desirable to recover hydraulic fluid which leaks past the sealing cup ll, and this is accomplished in the present construction. With each movement of the booster parts to the right to generate pressure in the high pressure end of the apparatus, air will flow into the space 6l to vent this space and to minimize leakage Past the Cup Tl. When the brakes are released the parts move back toward the left and air and any hydraulic brake fluid which may have leaked into the Space 87 will flow through the passage |25 and will unseat the valve t28. In this connection, it will be noted that Without the pipe lSB, the piston parts in Figure 2 would pump practically all of the hydraulic fluid out through the passage |25. As the fluid accumulates above the ball |28 subsequent applications of the brakes and the releasing of the brakes would gradually return this fluid through line |34 to the reservoir l.

However, to insurefagainst any leakage past the cup 8E, the pipe |3il is connected to the passage |33 which acts as a pump chamber in connection with the expansible and contractible chamber 55. Upon each releasing of the brakes, the space S expands, and the capacity of this space being greater than that of the space 81, a partial vacuum will be created in the space 8l' to draw fluid therefrom through passage and thus past the ball |28. The subsequent application of the brakes will cause contraction of the 'space 95 and air pumped therefrom through pipe |39 Will force accumulations of brake uuid below the valve |28 to unseat the ball |32 and flow through pipe |34 back into the reservoir Il.

Accordingly, it Will be apparent that the present construction not only minimizes leakage past the cup ll by maintaining substantially atmospheric pressure in the chamber 81, but also functions to return all leakage fluid to the reservoir H. Thus the leakage of hydraulic brake uid from the system does not exceed normal leakage occurring with conventional systems which do not employ booster mechanisms. The prevention of the loss of hydraulic fluid from the system thus maintains an adequate supply of hydraulic Huid over long periods of time whereas in conventional systems employing boosters, leakage occurs at a far faster rate. Ordinarily, therefore, it is necessary to check the supply of iluid in the reservoir quite often, otherwise the operator may rind himself unable to apply the brakes because of excessive loss of brake fluid from the system.

As previously stated, the opening |25 is provided for use when the apparatus is installed in vertical position With the right hand end as viewed in Figure l arranged at the top. When the device is arranged in the position shown in Figure l, hydraulic fluid in the space 81 will gravitate toward the passage |25 and may freely ncrv therethrough by virtue of the venting of the top of the space 8l to the atmosphere. With the apparatus arranged in vertical position, however, the leakage fluid in the space will gravitate toward the groove H. The suction created in the space |25 under such conditions will sometimes cause air from the passage H5 to mingle with and agitate the hydraulic fluid in the groove H8 and cause it to foam and somewhat interfere with the proper operation of the apparatus. It is accordingly preferred that the opening 25 be employed, in which case the passage H will be open to the space 3i above the level of hydraulic fluid therein, thus properly venting the space 8l for the flow of the hydraulic huid through passage 25.

The question of hydraulic fluid leakage past the seal ot in the low pressure end of the apparatus is less serious than that in the high pressure end. Some leakage into the space will occur, however, and any such leakage iluid may flow through opening |39 through passage |38 into the pipe E3B. Upon each movement of the piston 92 toward the right, such leakage iluid will be displaced into and through the pipe 38 and thus this uid will be saved together with the fluid leaking into the space 81, to be returned to the reservoir The additional cost of the present device over ccnventional booster mechanisms is slight since it employs only two sections of tubing and simple relatively inexpensive check valves. The Withdrawing of the leakage fluid from the space 8l and the pumping of such fluid back into the reservoir, in the present embodiment of the invention, utilizes the operation of parts of a conventional booster brake mechanism.

We claim:

1. A hydraulic booster brake system comprising 9, master cylinder having a reservoir, hydraulically operated Wheel cylinders for applying the brakes, a 10W pressure cylinder having one end connected to said master cylinder, a high pressure cylinder having one end connected to said Wheel cylinders, a piston sleeve in said high pressure cylinder, a tubular piston rod having a piston in said low pressure cylinder and a plunger in said piston sleeve, said tubular piston rod having an axial passage therethrough communicating between said ends of said cylinders, means for closing said axial passage upon movement of said piston away from said end of said low pressure cylinder incident to the flow of hydraulic fluid thereinto from said master cylinder, a booster motor connected to said piston sleeve, control means for energizing said motor upon said movement of said piston to actuate said piston sleeve whereby it cooperates with said plunger to generate pressure in said end of said high pressure cylinder, a seal in the other end of said low pressure cylinder surrounding said tubular piston rod whereby said other end of said low pressure cylinder becomes an expansible chamber device, a duct connecting the other end of said high pressure cylinder to said expansible chamber device, a pipe connecting said duct to said reservoir, a check valve in said duct between said pipe and said other end of said high pressure cylinder and opening away from the latter, and a check valve in said pipe opening toward said reservoir.

2. A hydraulic iiuid pressure mechanism comprising a cylinder, a piston in said cylinder, means for maintaining one end of said cylinder full of hydraulic fluid and said piston being movable toward said end of said cylinder to generate pressure in said fluid, a seal in the other end of said cylinder surrounding said piston, an inwardly opening check valve connected to said other end of said cylinder inwardly of said seal for admitting air thereinto during pressure-generating movement of said piston, and an expansible chamber device having mechanical connection with said piston and operable during movement of said piston toward said other end of said cylinder for withdrawing hydraulic iiuid therefrom.

3. A hydraulic uid pressure mechanism comprising a cylinder, a piston in said cylinder, means for maintaining one end of said cylinder full of hydraulic iiuid and said piston being movable toward said end of said cylinder to generate pressure in said fluid, a seal in the other end of said cylinder surrounding said piston, an inwardly opening check valve connected to said other end of said cylinder inwardly of said seal for admitting air thereinto during pressure-generating movement of said piston, a reservoir for supplying hydraulic fluid to said iirst named end of said cylinder, and means having mechanical connection with said piston and operative during movement of said piston toward said other end of said cylinder for withdrawing hydraulic fluid therefrom, and operative thereafter for returning such hydraulic fluid to said reservoir.

4. A hydraulic fluid pressure mechanism comprising a cylinder, a piston in said cylinder, means for maintaining one end of said cylinder full of hydraulic fluid and said piston being movable toward said end of said cylinder to generate pressure in said fluid, a seal in the other end of said cylinder surrounding said piston, an inwardly opening check Valve connected to said other end of said cylinder inwardly of said seal foradmitting air thereinto during pressure-generating movement of said piston, an expansible chamber device connected `xto and operable coincidentally with said piston, a duct connecting said expansible chamber device to said other end of said cylinder to withdraw hydraulic fluid therefrom during movement of said piston toward said other end of said cylinder, a check valve in said duct opening away from said cylinder, and a pipe connecting said duct to said reservoir and having a check valve therein opening toward said reservoir, whereby said expansible chamber device, during pressure-generating movement of said piston returns hydraulic fluid from said duct through said pipe to said reservoir.

5. A hydraulic mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate hydraulic pressure therein, sealing means in the other end of said cylinder surrounding said piston, a duct connected at one end to the space provided in said other end of said cylinder inwardly of said sealing means, and an expansible chamber device comprising a chamber and a member movable to vary the capacity thereof, such member being connected to and operative coincidentally with said piston and connected to said duct, said expansible chamber device expanding its capacity as said piston moves toward said other end of said cylinder, at a rate greater than the reduction in the capacity of said space.

6. A hydraulic mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate hydraulic pressure therein, sealing means in the other end of said cylinder surrounding said piston, a duct connected at one end to the space provided in said other end of said cylinder inwardly of said sealing means, an expansible chamber device having a chamber connected to said duct, and

-means having mechanical connection withsaid piston and operable coincidentally therewith for expanding said chamber during reduction of the capacity of said space during movement of said piston toward said other end of said cylinder, said chamber having a rate of capacity increase exceeding the rate of capacity decrease of said space.

7. A hydraulic mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate hydraulic pressure therein, sealing means in the other end of said cylinder surrounding said piston, a duct connected at one end to the space provided in said other end of said cylinder inwardly of said sealing means, an expansible chamber device having a chamber connected to said duct, means having mechanical connection with said piston and operable coincidentally therewith for expanding said chamber during reduction of the capacity of said space during movement of said piston toward said other end of said cylinder, said chamber having a rate of capacity increase exceeding the rate of capacity decrease of said space, a reservoir for supplying hydraulic fluid to said one end of said cylinder, a pipe connecting said duct to said reservoir, and check valves in said duct and said pipe, the means for expanding said chamber operating to reduce the capacity thereof during movement of said piston in pressure-generating movements thereof for returning hydraulic fluid to said reservoir throughsaid pipe.

8. A hydraulic mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generatehydraulicpressure therein, sealing means in the other end of said cylinder surrounding said piston, a fluid pressure motor at said other end of said cylinder, said motor comprising a casing section coaxial with said cylinder and further comprising a pressure responsive unit connected to said piston to effect pressure generating movement thereof, a duct connected at one end to the space provided in said other end of said cylinder between said sealing means and said piston, and an expansible Chamber device comprising a chamber and a member movable to vary the capacity thereof, such member haring mechanical connection with and operative coincidentally with said piston and said chamber being connected to the other end of said duct.

9. A hydraulic mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate hydraulic pressure therein, sealing means in the other end of said cylinder surrounding said piston, a fluid pressure motor at said other end of said cylinder, said motor comprising a casing section coaxial With said cylinder and further comprising a pressure responsive unit connected to said piston to effect pressure generating movement thereof, a duct connected at one end to the space provided in said other end of said cylinder between said sealing means and said piston, an expansible chamber device having a chamber connected to said duct, and means having mechanical connection with said piston and operable coincidentally therewith for expanding said chamber during reduction of the capacity of said space during movement of said piston toward said other end o f said cylinder, said chamber having a rate of capacity increase exceeding the rate of capacity decrease of said space.

10. A hydraulic booster brake mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate pressure therein, a vacuum booster, motor having a pressure movable element connected to said piston to move it toward said end of said cylinder upon energization of said motor, said pressure movable element dividing said motor into a pair of iluid pressure chambers one of Which is adjacent the other end oi said cylinder and is subject to connection with a source of vacuum, a seal in said other end of said cylinder sealing the interior of said other end of said cylinder from said one chamber, a duct communicating With the interior oi said other end of said cylinder between said seal and said piston, and means for creating a relatively low pressure in said duct for Withdrawing therethrough any hydraulic fluid leaking past said piston into said other end of said cylinder.

11. A hydraulic booster brake mechanism comprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate pressure therein, a vacuum booster motor havinga pressure movable element connected to said piston to move it toward said end of said cylinder upon energization of said motor, said pressure movable element dividing said motor into a pair of uid pressure chambers one of which is adjacent'the other end vof said cylinder and is subject to connection with a source of vacuum, a seal in said other end of said cylinder sealing the in.- terior of said other end of said cylinder from said one chamber, a duct communicating with the interior of said other end of said cylinder between said seal and said piston, and an expansible chamber device comprising a chamber connected to the other end of said duct and a member movable to expand said chamber, such member having mechanical connection with said piston to be operated coincidentally therewith to expand said last-named chamber upon movement of said piston toward said other end of said cylinder.

12. A hydraulic booster brake mechanism cornprising a hydraulic cylinder, a piston in said cylinder movable toward one end thereof to generate pressure therein, a vacuum booster motor having a pressure movable element connected to said piston to move it toward said end of said cylinder upon energization oi said motor, said pressure movable element dividing said motor into a pair of iluid pressure chambers one of Which is adjacent the other end of said cylinder and is subject to connection with a source of vacuum, a seal in said other end of said cylinder sealing the interior of said other end of said cylinder from said one chamber, a duct communicating with the interior of said other end of said cylinder between said seal and said piston, an expansible chamber device comprising a chamber connected to the other end of said duct and a member movable to expand said chamber, such member having mechanical connections with said piston to be operated coincidentally therewith to expand said last-named chamber upon movement of said piston toward said other end of said cylinder, a check valve providing for the flow of hydraulic fluid from said other end of said cylinder into said duct, a second duct communicating with said rstnamed duct between said Check valve and said expansible chamber device, and a check valve in said second duct opening away from said rstnamed duct.

References Cited in the ille of this patent UNITED STATES PATENTS Number Name Date 1,617,020 Merwin Feb. 8, 1927 1,653,276 Harris Dec. 20, 1927 1,978,667 Breese Oct. 30, 1934 2,140,733 Carroll Dec. 20, 1938 2,207,226 Schmidt July 9, 1940 2,222,848 La Brie Nov. 26, 1940 2,328,637 Freeman Sept. 7, 19a?, 2,344,768 Dodson Mar. 21, 1944 2,438,723 Stelzer Mar. 30, 1948 2,504,691 Ingres Apr. 18, 1950 

